One package, stable, moisture curable, polyalkoxy-terminated organopolysiloxane compositions and method for making

ABSTRACT

Stable, substantially acid-free, one package moisture curable polyalkoxy-terminated organopolysiloxane compositions are provided having a condensation catalyst such as a tin compound. A method for making the aforesaid moisture curable organopolysiloxane compositions, is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to copending application Ser. No. 277,525, filed June26, 1981, now U.S. Pat. No. 4,377,706, of John E. Hallgren, forDialkoxysilylenolethers and method for making.

BACKGROUND OF THE INVENTION

Prior to the present invention, various one and two-package moisturecurable room temperature vulcanizable (RTV) compositions were availablebased on the use of a silanol-terminated polydiorganosiloxane having theformula, ##STR1## where R is a C.sub.(1-13) monovalent substituted orunsubstituted hydrocarbon radical, which is preferably methyl, or amixture of a major amount of methyl and a minor amount of phenyl,cyanoethyl, trifluoropropyl, vinyl, and mixtures thereof and n is aninteger having a value of from about 50 to about 2500, with across-linking silane having hydrolyzable radicals attached to silicon.

For example, Ceyzeriat, U.S. Pat. No. 3,133,891 and Bruner, U.S. Pat.No. 3,035,016, are based on the use of methyltriacetoxysilane with asilanol-terminated polydimethylsiloxane under substantially anhydrousconditions. Although the one-package compositions of Bruner orCeyzeriat, upon exposure to atmospheric moisture, provide satisfactoryone-package room temperature vulcanizable organopolysiloxanecompositions exhibiting satisfactory tack-free time, for example, 30minutes or less after an extended shelf period, the acetic acidby-product is corrosive and has a disagreeable odor.

Other variations of one-package acyloxy acid generating RTV's are shownby Kulpa, U.S. Pat. No. 3,296,161, Goossens, U.S. Pat. No. 3,296,195 andBeers, U.S. Pat. No. 3,438,930, assigned to the same assignee as thepresent invention. Additional one-package acyloxy acid generating RTVcompositions are shown by Schulz et al, U.S. Pat. No. 3,647,917 andNitzsche et al U.S. Pat. No. 3,886,118.

An improved, low odor, substantially non-corrosive one-package RTVcomposition is shown by Beers, U.S. Pat. No. 4,257,932, assigned to thesame assignee as the present invention. Beers achieves a reduction inodor and corrosive properties by utilizing as a crosslinking silane aless volatile material such as methyltris-(2-ethylhexanoxy)silane.

A non-corrosive two package moisture curable organopolysiloxanecomposition free of carboxylic acid generating groups is shown byNitzsche et al, U.S. Pat. No. 3,127,363 which is based on the use of apolyalkoxysilane, or polysilicate cross linking agent, in place ofmethyltriacetoxysilane. The ingredients of the two package noncorrosivecomposition of Nitzsche et al, are mixed under atmospheric conditionsand the resulting composition must be used soon after the ingredientsare mixed because the resulting blend has a short shelf life. Althoughthe mixture of Nitzsche et al, which is typically polyalkoxysilane,silanol-terminated polydiorganosiloxane and tin soap catalyst, providesupon mixing, a fast curing non-corrosive room temperature vulcanizablecomposition, the Nitzsche et al mixture does not have the extended shelflife advantage of the one package system which is required forcommercial use and therefore is excluded from a variety of applications.

Nitzsche et al, U.S. Pat. No. 3,065,194, teaches that a mixture of anendblocked dimethylsiloxane polymer, such as hydroxy and alkoxyendblocked, inert filler, ethylorthosilicate and dibutyltindilaurate canbe vulcanized upon contact with water, after a 14 day shelf period atroom temperature. However, the various ingredients of the mixture haveto be vigorously dried by heating for 1 hour at 200° C., and the RTV,after a relatively short shelf period, has to be drenched with water.

Improved results toward combining the advantages of a non-corrosiveacid-free polyalkoxysilane cross-linking agent with a silanol-terminatedpolydiorganosiloxane as a one-package system are shown by Weyenberg,U.S. Pat. No. 3,334,067, Cooper et al, U.S. Pat. No. 3,542,901 and bySmith et al U.S. Pat. Nos. 3,689,454, and 3,779,986, the last two beingassigned to the same assignee as the present invention, utilizing atitanium chelate catalyst in place of a tin catalyst. However, afterroom temperature vulcanizable one-package systems based on a titaniumchelate catalyst were allowed to age for a period of 5 hours or more, itwas found that the tack-free time of the aged RTV was considerablylonger than the tack-free time of the same mixture after it wasinitially mixed and immediately exposed to atmospheric moisture.

As shown by Brown et al U.S. Pat. No. 3,122,522 a platinum catalyst isused to prepare an alkoxy terminated silalkylenepolysiloxane polymer.However, this method of synthesizing the base polymer requires anexpensive hydrosilylation procedure. Additional efforts to achieve adesirable non-corrosive, substantially odor-free stable one-package RTVbased on the use of polyalkoxy organopolysiloxane in a more economicmanner are shown by Brown et al, U.S. Pat. No. 3,161,614 or U.S. Pat.No. RE 29760. Brown et al employed a polyalkoxy end blocked polysiloxanewhich was based on the use of a mineral acid generatingpolyalkoxyhalosilane, and a curing catalyst. However, these compositionswere found to be unusable because they failed to cure in contact with atin catalyst, even in the presence of moisture.

As utilized hereinafter, the term "stable" as applied to the one packagepolyalkoxy-terminated organopolysiloxane RTV's of the present inventionmeans a moisture curable mixture capable of remaining substantiallyunchanged while excluded from atmospheric moisture and which cures to atack-free elastomer after an extended shelf period. In addition, astable RTV also means that the tack-free time exhibited by freshly mixedRTV ingredients under atmospheric conditions will be substantially thesame as that exhibited by the same mixture of ingredients exposed toatmospheric moisture after having been held in a moisture resistant andmoisture-free container for an extended shelf period at ambientconditions, or an equivalent period based on accelerated aging at anelevated temperature.

The present invention is based on the discovery that stable,substantially acid-free, one-package, moisture curablepolyalkoxy-terminated organopolysiloxane RTV compositions can be made byusing a silanol terminated polydiorganosiloxane consisting essentiallyof chemically combined diorganosiloxy units of the formula ##STR2## suchas a silanol-terminated polydiorganosiloxane of formula (1), where R isas previously defined, with an effective amount of certain silanescavengers for chemically combined hydroxy radicals. In thesilanol-terminated polydiorganosiloxane consisting essentially ofchemically combined formula (2) units, the presence of silicon bondedC.sub.(1-8) alkoxy radicals such as methoxy radical is not precluded.The hydroxy radicals which can be removed by the silane scavenger can befound in materials normally present in the RTV composition of thepresent invention, for example, trace amounts of water, methanol,silanol radicals on the silica filler (if used), the silanol polymer offormula (1), or a silanol-terminated polymer having formula (2) units.The silane scavenger useful for eliminating chemically combined hydroxyradicals in accordance with the practice of the invention preferably hasthe formula, ##STR3## where R¹ is a C.sub.(1-8) aliphatic organicradical selected from alkyl radicals, alkylether radicals, alkylesterradicals, alkylketone radicals, alkylcyano radicals or a C.sub.(7-13)aralkyl radical, R² is a C.sub.(1-13) monovalent organic radicalselected from R radicals as previously defined, and defined moreparticularly below, X is a hydrolyzable leaving group selected fromamido, amino, carbamato, enoxy, imidato, isocyanato, oximato,thioisocyanato, and ureido radicals. The preferred members are amino,amido, enoxy, and the more preferred is amido, for example,N-C.sub.(1-8) alkyl-C.sub.(1-8) acylamido, a is an integer equal to 1 or2 and preferably 1, b is a whole number equal to 0 or 1 and the sum ofa+b is equal to 1 or 2. In formula (3), where a is 2, X can be the sameor different. The leaving group X reacts preferentially before --OR¹with available --OH in the RTV composition and provides an RTVcomposition substantially free of halogen acid, or carboxylic acid. Thesilane scavenger of formula (3) is both the silane scavenger for hydroxyfunctional groups and a polyalkoxysilane cross-linking agent forterminating the silicon atom at each organopolysiloxane chain-end withat least two alkoxy radicals.

Among the ingredients of the RTV compositions which are formed as aresult of the use of the hydroxy scavenger of formula (3), issilanol-free polydiorganosiloxane, chain-terminated with two or three--OR¹ radicals. The silanol-free polydiorganosiloxane optionally can becombined with an effective amount of a cross-linking silane, as definedhereinafter, under substantially anhydrous conditions. The cross-linkingpolyalkoxysilane which can be utilized in combination with thescavenging silane of formula (3) has the formula, ##STR4## where R¹, R²and b are as previously defined. The preferred condensation catalystswhich can be used in the practice of the invention include metalcompounds selected from tin compounds, zirconium compounds, and titaniumcompounds or mixtures thereof. Additional condensation catalysts whichcan be used are defined more particularly hereinafter.

It is not completely understood why the polyalkoxy-terminatedorganopolysiloxane compositions of the present invention are stable inthe presence of certain condensation catalysts over an extended periodof time in the substantial absence of moisture.

A mechanistic study of the RTV of the present invention supports thetheory that the use of scavenging silane of formula (3) or (5) below orin combinations thereof with crosslinking silane of formula (4), inaccordance with the practice of the invention, minimize the likelihoodthat detrimental amounts of R¹ OH will be generated during the shelfperiod. R¹ OH generation is to be avoided because R¹ OH endstops thesilanol polymer of formula (1) or polymer with formula (2) units toproduce polymers having terminal ##STR5## units. These polymers, whereinthe silicon atom at each polymer chain end is terminated with only onealkoxy radical, have slow cure times. In addition, R¹ OH can breakdownthe organopolysiloxane polymer in the presence of the condensationcatalyst.

The aforedescribed one package RTV compositions of Brown et al areunstable. In Brown et al, which uses chloroalkoxysilanes, the chlororadical is the leaving group. It has been found that chloro radicalleaving groups can form highly corrosive halogen acids, or halogen acidamine salts, when used with an acid acceptor, such as pyridine.

The use of the silane scavenger for hydroxy of formulas (3) or (5), inwhich the leaving group X is not a halogen radical, substantiallyeliminates undesirable water in the filler and silicone polymer, as wellas residual moisture in the RTV composition during the shelf period. Indetermining what level of silane scavenger of formula (3) or (5) to usein the practice of the invention, the total hydroxy functionality of theRTV composition can be estimated. The total hydroxy functionality of thepolymer can be determined by infrared analysis. In order to insure thatan effective or stabilizing amount of scavenger is used to maintain thestability of the composition over an extended shelf period of six monthsor more at ambient temperature while in a sealed container, there can beused an additional amount of scavenger over that amount required toendstop the polymer. This excess of scavenger can be up to about 3% byweight, based on the weight of the polymer. The aforementioned 3% ofscavenger by weight exceeds that amount required to substantiallyeliminate available hydroxy functionality in the polymer as a result ofreaction between OH functionality and X radicals. In compositions whichalso contain filler and other additives, the additional amount ofscavenger of formulas (3) or (5) which is required is estimated byrunning a 48 hour stability check at 100° C. to determine whether thetack-free time remains substantially unchanged as compared to thetack-free time of the composition before aging measured undersubstantially the same conditions.

Where polyalkoxy-terminated polymer of formula (6) below is made withoutusing silane scavenger of formula (3), silane scavenger can be used inthe practice of the invention having less than two--OR¹ radicalsattached to silicon, as shown by the formula, ##STR6## where R¹, R², andX are as previously defined, c is a whole number equal to 0 to 3inclusive, d is an integer equal to 1 to 4 inclusive, and the sum of(c+d) is equal to 3 or 4. In such situations, the scavenging silanes offormula (5) can be used in an amount sufficient to stabilize the RTVcomposition as previously defined for the scavenging silane of formula(3). In addition, there can be used with scavengers of formulas (3) or(5) at least 0.01 part and up to 10 parts of the cross-linking silane offormula (4).

The polyalkoxy-terminated organopolysiloxane of the present inventionhas the formula, ##STR7## where R, R¹, R², X, n and b are as previouslydefined and e is equal to 0 to 1 and the sum of b+e is equal to 0 to 1.The polyalkoxy-terminated organopolysiloxane of formula (6), can be madeby various procedures. One procedure is taught by Cooper et al U.S. Pat.No. 3,542,901 involving the use of a polyalkoxysilane with asilanolterminated polydiorganosiloxane in the presence of an aminecatalyst. A method not taught by Cooper et al is the use of the silanescavenger of formula (3) as an end-capper with silanol-terminatedpolydiorganosiloxane used in the practice of the invention.

In formulas (1-6), R is preferably selected from C.sub.(1-13) monovalenthydrocarbon radicals, halogenated hydrocarbon radicals and cyano alkylradicals, R¹ is preferably a C.sub.(1-8) alkyl radical or a C.sub.(7-13)aralkyl radical, R² is preferably methyl, phenyl, or vinyl.

The preferred X radicals in formulas 3, 5 and 6 are amido, amino andenoxy, and the most preferred is amido.

The expression "substantially acid-free" with respect to defining theelastomer made from the RTV composition of the present invention uponexposure to atmospheric moisture means yielding by-products having a pKaof 5.5 or greater with 6 or greater preferred and 10 or greater beingparticularly preferred.

It has been further found that improved cure rates can be achieved ifminor amounts of amines, substituted guanidines, or mixtures thereof,are utilized as curing accelerators in the polyalkoxy compositions ofthe present invention. These curing accelerators also serve to catalyzethe ability of the enoxy leaving group to act as a scavenger. There canbe used from 0.1 to 5 parts, and preferably from about 0.3 to 1 part ofcuring accelerator, per 100 parts of the silanol-terminated polymer offormula (1), or which consists of chemically combined units of formula(2), or 100 parts of the polyalkoxy-terminated polymer of formula (6) tosubstantially reduce the tack-free time (TFT) of the RTV composition ofthe present invention. This enhanced cure rate is maintained after ithas been aged for an extended shelf period, for example, 6 months ormore at ambient temperatures, or a comparable period under acceleratedaging conditions. Its cure properties after the extended shelf periodwill be substantially similar to its initial cure properties, forexample, tack-free time (TFT), shown by the RTV composition upon beingfreshly mixed and immediately exposed to atmospheric moisture.

It appears that the curing accelerators described herein, in addition todecreasing the tack-free times of the RTV compositions of thisinvention, also provide a surprising stabilizing effect for particularRTV compositions catalyzed with certain condensation catalysts whichexhibit a marked lengthening of tack-free time after accelerated aging.For this class of condensation catalysts, addition of amines,substituted guanidines and mixtures thereof described herein providestable RTV compositions which exhibit a fast cure rate initially, i.e.less than about 30 minutes which remains substantially unchanged afteraccelerated aging.

The RTV compositions of the present invention can cure to a depth of1/8" thickness within 24 hours. Durometer Hardness (Shore A) can then bedetermined and used to evaluate the cure of the compositions as shown inthe examples.

STATEMENT OF THE INVENTION

There is provided by the present invention, a one-package, substantiallyanhydrous, room temperature vulcanizable organopolysiloxane compositionstable under ambient conditions in the substantial absence of moistureover an extended period of time and convertible to a substantiallyacid-free, tack-free elastomer comprising, (1) an organopolysiloxanewherein the silicon atom at each polymer chain end is terminated with atleast two alkoxy radicals, (2) an effective amount of condensationcatalyst and (3) a stabilizing amount of scavenging silane of theformula, ##STR8## where R¹, R², X and c are as previously defined, f isan integer equal to 1 to 4 inclusive, and the sum of c+f is equal to 1to 4 inclusive. In addition, an effective amount of a curing acceleratorselected from substituted guanidines, amines and mixtures thereof isused.

In a further aspect of the present invention, there is provided a stableroom temperature vulcanizable polyalkoxy-terminated organopolysiloxanecomposition curable under ambient conditions to a tack-free,substantially acid-free elastomer comprising,

(A) 100 parts of a polyalkoxy-terminated organopolysiloxane of formula(6)

(B) 0 to 10 parts of a cross-linking silane of formula (4),

(C) an effective amount of condensation catalyst, and

(D) a stabilizing amount of scavenging silane of formula (7).

Also included within the scope of the present invention is a method ofmaking a room temperature vulcanizable organopolysiloxane compositionunder substantially anhydrous conditions utilizing an effective amountof a condensation catalyst with a silanol-terminated organopolysiloxaneand a polyalkoxysilane cross-linking agent, the improvement whichcomprises (1) adding to the silanol-terminated organopolysiloxane astabilizing amount of a polyalkoxysilane which is both a scavenger forhydroxy functional groups and a cross-linking agent of the formula##STR9## where R¹, R², X, a and b are as previously defined, andthereafter adding an effective amount of a condensation catalyst,whereby improved stability is achieved in the resulting room temperaturevulcanizable organopolysiloxane composition.

Another method of the present invention is making a room temperaturevulcanizable organopolysiloxane composition under substantiallyanhydrous conditions utilizing an effective amount of a condensationcatalyst with an organopolysiloxane wherein the silicon atom at eachpolymer chain end is terminated with at least two alkoxy radicals, whichinvolves the improvement which comprises adding to saidpolyalkoxy-terminated organopolysiloxane (1) a stabilizing amount of asilane scavenger for hydroxy functional groups of the formula, ##STR10##where R¹, R², X, c and f are as previously defined and (2) an effectiveamount of a condensation catalyst, whereby improved stability isachieved in the resulting room temperature vulcanizableorganopolysiloxane composition.

In an additional aspect of the present invention, there is provided amethod of making a stable, one-package room temperature vulcanizablepolyalkoxyterminated organopolysiloxane composition which comprisesagitating, under substantially anhydrous conditions, a room temperaturevulcanizable material selected from

(i) a mixture comprising on a weight basis

(a) 100 parts of a silanol-terminated polydiorganosiloxane consistingessentially of chemically combined units of formula (2),

(b) an amount of silane of formula (3) sufficient to scavenge available--OH in the RTV composition and provide up to 3% by weight excess, basedon the weight of RTV composition,

(c) 0 to 10 parts of the cross-linking silane of formula (4),

(d) an effective amount of a condensation catalyst, and

(e) 0 to 5 parts of curing accelerator selected from substitutedguanidines, amines and mixtures thereof wherein, the condensationcatalyst is added after the silanol-terminated polydiorganosiloxane andscavenging silane are mixed; and

(ii) a mixture comprising,

(a) 100 parts of the polyalkoxy-terminated organopolysiloxane of formula(6),

(b) 0 to 10 parts of the cross-linking silane of formula (4),

(c) an effective amount of a condensation catalyst,

(d) a stabilizing amount of silane scavenger of formula (7), and

(e) 0 to 5 parts of curing accelerator selected from substitutedguanidines, amines and mixtures thereof.

Radicals included within R of formulas (1), (2) and (6) are, forexample, aryl radicals and halogenated aryl radicals, such as phenyl,tolyl, chlorophenyl, naphthyl; aliphatic and cycloaliphatic radicals,for example, cyclohexyl, cyclobutyl; alkyl and alkenyl radicals, such asmethyl, ethyl, propyl, chloropropyl, vinyl, allyl, trifluoropropyl; andcyanoalkyl radicals, for example, cyanoethyl, cyanopropyl, cyanobutyl.Radicals preferably included within R¹ are, for example, C.sub.(1-8)alkyl radicals, for example, methyl, ethyl, propyl, butyl, pentyl;C.sub.(7-13) aralkyl radicals, for example, benzyl; phenethyl;alkylether radicals such as 2-methoxyethyl; alkylester radicals, forexample 2-acetoxyethyl; alkylketone radicals, for example1-butan-3-onyl; alkylcyano radicals, for example 2-cyanoethyl. Radicalsincluded within R² are the same or different radicals included within Rradicals. In formulas (1-7) where R, R¹, and R², can be more than 1radical, these radicals can be the same or different.

Some of the scavengers for chemically combined hydroxy radicals includedwithin one or more of formulas (3), (5), and (7), are, for example,

Oximatosilanes such as,

methyldimethoxy(ethylmethylketoximo)silane;

methylmethoxybis-(ethylmethylketoximo)silane;

methyldimethoxy(acetaldoximo)silane.

Carbamatosilanes such as,

methyldimethoxy(N-methylcarbamato)silane;

ethyldimethoxy(N-methylcarbamato)silane.

Enoxysilanes such as,

methyldimethoxyisopropenoxysilane;

trimethoxyisopropenoxysilane;

methyltri-iso-propenoxysilane;

methyldimethoxy(but-2-ene-2-oxy)silane;

methyldimethoxy(1-phenylethenoxy)silane;

methyldimethoxy-2(1-carboethoxypropenoxy)silane.

Aminosilanes such as,

methylmethoxydi-N-methylaminosilane; vinyldimethoxymethylaminosilane;tetra-N,N-diethylaminosilane

methyldimethoxymethylaminosilane; methyltricyclohexylaminosilane;

methyldimethoxyethylaminosilane; dimethyldi-N,N-dimethylaminosilane;

methyldimethoxyisopropylaminosilane dimethyldi-N,N-diethylaminosilane.

Amidosilanes such as,

ethyldimethoxy(N-ethylpropionamido)silane;

methyldimethoxy(N-methylacetamido)silane;methyltris(N-methylacetamido)silane;

ethyldimethoxy(N-methylacetamido)silane;methyltris(N-methylbenzamido)silane;

methylmethoxybis(N-methylacetamido)silane;

methyldimethoxy(caprolactamo)silane.

trimethoxy(N-methylacetamido)silane.

Imidatosilanes such as,

methyldimethoxyethylacetimidatosilane;

methyldimethoxypropylacetimidatosilane.

Ureidosilanes such as,

methyldimethoxy(N,N',N'-trimethylureido)silane;

methyldimethoxy(N-allyl-N',N'-dimethylureido)silane;

methyldimethoxy(N-phenyl-N',N'-dimethylureido)silane.

Isocyanatosilanes such as,

methyldimethoxyisocyanatosilane;

dimethoxydiisocyanatosilane.

Thioisocyanatosilanes such as,

methyldimethoxythioisocyanatosilane;

methylmethoxydithioisocyanatosilane.

In addition, formula (5) scavenging silanes include silanes such asmethyltris(N-methylacetamido)silane; tetra(isopropenoxy)silane. Alsoincluded are silanes having different leaving groups such asdiethylamino(N-methylcarbamato)isopropenoxy(N-allyl-N',N'-dimethylureido)silane.

Some of the cross-linking polyalkoxysilanes included within formula (4)are, for example, methyltrimethoxysilane; methyltriethoxysilane;ethyltrimethoxysilane; tetraethoxysilane; vinyltrimethoxysilane; etc.

Among the curing accelerators which can be used in the practice of theinvention are silyl substituted guanidines having the formula,

    (Z).sub.g Si(OR.sup.1).sub.4-g,                            (8)

where R¹ is as previously defined, Z is a guanidine radical of theformula, ##STR11## R³ is divalent C.sub.(2-8) alkylene radical, R⁴ andR⁵ are selected from hydrogen and C.sub.(1-8) alkyl radicals and g is aninteger equal to 1 to 3 inclusive. In addition, alkyl substitutedguanidines having the formula, ##STR12## where R⁴ and R⁵ are aspreviously defined and R⁶ is a C.sub.(1-8) alkyl radical, also can beemployed. Some of the silyl substituted guanidines included withinformula (8) are shown by Takago U.S. Pat. Nos. 4,180,642 and 4,248,993.

In addition to the above substituted guanidines, there can be usedvarious amines, for example, di-n-hexylamine, dicyclohexylamine,di-n-octylamine, hexamethoxymethylmelamine, and silylated amines, forexample, γ-aminopropyltrimethoxysilane andmethyldimethoxy-di-n-hexylaminosilane.Methyldimethoxy-di-n-hexylaminosilane acts as both a scavenger andcuring accelerator. The primary amines, secondary amines, silylatedsecondary amines are preferred, and secondary amines, and silylatedsecondary amines are particularly preferred. Silylated secondary aminessuch as alkyldialkoxy-n-dialkylaminosilanes and guanidines such asalkyldialkoxyalkylguanidylsilanes which are useful as cure acceleratorsherein also act as scavengers and, in certain instances, as stabilizersin the compositions of this invention.

Silanol-terminated polydiorganosiloxanes of formula (1), as well assilanol terminated silicone polymers consisting essentially of formula(2) units are well known and preferably have a viscosity in the range offrom about 100 to about 400,000 centipoise and more preferred from about1000 to about 250,000 centipoise when measured at about 25° C. Thesesilanol-terminated fluids can be made by treating a higher molecularweight organopolysiloxane, such as dimethylpolysiloxane with water inthe presence of a mineral acid, or base catalyst, to tailor theviscosity of the polymer to the desired range. Methods for making suchhigher molecular weight organopolysiloxane utilized in the production ofsilanol-terminated polydiorganosiloxane of formula (1), or havingchemically combined formula (2) units, also are well known. For example,hydrolysis of a diorganohalosilane such as dimethyldichlorosilane,diphenyldichlorosilane, methylvinyldichlorosilane, or mixtures thereof,can provide for the production of low molecular weight hydrolyzate.Equilibration thereafter can provide for higher molecular weightorganopolysiloxane. Equilibration of cyclopolysiloxane such asoctamethylcyclotetrasiloxane, octaphenylcyclotetrasiloxane, or mixturesthereof, will also provide for higher molecular weight polymers.Preferably, such polymers are decatalyzed of equilibration catalyst bystandard procedures prior to use, such as shown by Boot U.S. Pat. No.3,153,007, assigned to the same assignee as the present invention.

Silanol-terminated organopolysiloxanes having viscosities below 1200centipoises can be made by treating organopolysiloxanes consistingessentially of chemically combined diorganosiloxy units with steam underpressure. Other methods that can be employed to make silanol-terminatedpolydiorganosiloxanes are more particularly described in U.S. Pat. No.2,607,792 to Warrick and U.K. Pat. No. 835,790.

Effective amounts of the condensation catalysts which can be used in thepractice of the present invention to facilitate the cure of the RTVcompositions are, for example, 0.001 to 1 part based on the weight of100 parts of the silanol-terminated polydiorganosiloxane of formula (1).There are included tin compounds, for example, dibutyltindilaurate;dibutyltindiacetate; dibutyltindimethoxide; carbomethoxyphenyl tintris-uberate; tin octoate; isobutyl tin triceroate; dimethyl tindibutyrate; dimethyl tin di-neodecanoate; triethyl tin tartrate; dibutyltin dibenzoate; tin oleate; tin naphthenate; butyltintri-2-ethylhexoate;tinbutyrate. The preferred condensation catalysts are tin compounds anddibutyltindiacetate is particularly preferred.

Titanium compounds which can be used are, for example,1,3-propanedioxytitanium bis(ethylacetoacetate);1,3-propanedioxytitanium bis(acetylacetonate); diisopropoxytitaniumbis(acetylacetonate); titanium naphthenate; tetrabutyltitanate;tetra-2-ethylhexyltitanate; tetraphenyltitanate; tetraoctadecyltitanate;ethyltriethanolaminetitanate. In addition beta-dicarbonyltitaniumcompounds as shown by Weyenberg U.S. Pat. No. 3,334,067 can be used ascondensation catalysts in the present invention.

Zirconium compounds, for example, zirconium octoate, also can be used.

Further examples of metal condensation catalysts are, for example, lead2-ethyloctoate; iron 2-ethylhexoate; cobalt 2-ethylhexoate; manganese2-ethylhexoate; zinc 2-ethylhexoate; antimony octoate; bismuthnaphthenate; zinc naphthenate; zinc stearate.

Examples of nonmetal condensation catalysts are hexylammonium acetateand benzyltrimethylammonium acetate.

Various fillers and pigments can be incorporated in the silanol oralkoxy-terminated organopolysiloxane, such as for example, titaniumdioxide, zirconium silicate, silica aerogel, iron oxide, diatomaceousearth, fumed silica, carbon black, precipitated silica, glass fibers,polyvinyl chloride, ground quartz, calcium carbonate etc. The amounts offiller used can obviously be varied within wide limits in accordancewith the intended use. For example, in some sealant applications, thecurable compositions of the present invention can be used free offiller. In other applications, such as the employment of the curablecompositions for making binding material on a weight basis, as much as700 parts or more of filler, per 100 parts of organopolysiloxane can beemployed. In such applications, the filler can consist of a major amountof extending materials, such as ground quartz, polyvinylchloride, ormixtures thereof, preferably having an average particle size in therange of from about 1 to 10 microns.

The compositions of the present invention also can be employed asconstruction sealants and caulking compounds. The exact amount offiller, therefore, will depend upon such factors as the application forwhich the organopolysiloxane composition is intended, the type of fillerutilized (that is, the density of the filler and its particle size).Preferably, a proportion of from 10 to 300 parts of filler, which caninclude up to about 35 parts of a reinforcing filler, such as fumedsilica filler, per 100 parts of silanol-terminated organopolysiloxane isutilized.

In the practice of the invention, the room temperature vulcanizablecompositions can be made by agitating, for example stirring, a mixtureof materials which can consist of the silanol terminatedpolydiorganosiloxane, which hereinafter will include formula (1) orpolymer consisting essentially of formula (2) units along with thescavenging silane of formula (3), and crosslinking silane of formula(4), which can be optional, where the blending is performed in thesubstantial absence of atmospheric moisture. Thereafter the condensationcatalyst is added also in the substantial absence of atmosphericmoisture.

As used hereinafter, the expressions "moisture-free conditions" and"substantially anhydrous conditions", with reference to making the RTVcompositions of the present invention, mean mixing in a dry box, or in aclosed container which has been subjected to vacuum to remove air, whichthereafter is replaced with a dry inert gas, such as nitrogen.Experience has shown that sufficient scavenging silane of formula (3)should be utilized as previously defined. Temperatures can vary fromabout 0° C. to about 180° C. depending upon the degree of blending, thetype and amount of filler.

A preferred procedure for making the RTV composition of the presentinvention is to agitate under substantially anhydrous conditions, amixture of the silanol terminated polydiorganosiloxane, filler and aneffective amount of the scavenging silane of formula (3) sufficient toeffect the substantial elimination of hydroxy functional radicals and toend cap the polymer. This "end capping" and scavenging procedure canrequire several minutes, hours, or even days, depending upon suchfactors as the nature of the X leaving group, the number of --OR¹radicals on the scavenging silane, etc. There then can be added to thesubstantially silanol-free mixture, the condensation catalyst, thecross-linking silane, or mixture thereof, along with other ingredients,for example, the curing accelerator and pigments. A stabilizing excessof the scavenging silane can be used in the initial or final stages ofthe mixing procedure if desired in amounts previously defined.

In instances where the polyalkoxy-terminated organopolysiloxane offormula (6) is made by a procedure not requiring the use of scavengingsilane of formula (3), stabilizing amounts of scavenging silane shown byformulas (5) or (7) can be used. Here, the scavenging silane can beadded before, with, or after the addition of condensation catalyst.Alternative procedures for making polyalkoxy-terminatedorganopolysiloxane are shown as previously indicated by Cooper et al,U.S. Pat. No. 3,542,901.

In order that those skilled in the art will be better able to practicethe present invention, the following examples are given by way ofillustration and not by way of limitation. All parts are by weightunless otherwise indicated.

EXAMPLE 1

Room temperature vulcanizable one-package RTV compositions were preparedunder substantially anhydrous conditions utilizing a dry nitrogenatmosphere after the ingredients had been stripped of air and volatilesunder reduced pressure, at ambient temperatures. There was stirred for15 minutes 100 parts of a silanol-terminated polydimethylsiloxane havinga viscosity of about 2500 centipoise and 0.09% by weight of hydroxyradicals attached to silicon with 3.4 parts ofmethyldimethoxy-(N-methylacetamido)silane. Based on method ofpreparation there was obtained a dimethoxy-terminatedpolydimethylsiloxane of the formula, ##STR13##

In an alternative procedure, methyldimethoxychlorosilane was used as achain terminator. This compound is shown by Brown et al, U.S. Pat. No.RE.29760. There was mixed under substantially anhydrous conditions, 6parts of methyldimethoxychlorosilane, 100 parts of the above describedsilanol-terminated silane, 6 parts of pyridine and 200 parts of toluenefor a period of 30 minutes. There was then added 2 parts of methanol tothe mixture. The mixture was then stirred for 30 minutes. The solidswere removed and the mixture was stripped.

There was added 0.13 part of dibutyltindimethoxide under substantiallyanhydrous conditions to the respective dimethoxy-terminatedpolydimethylsiloxanes made withmethyldimethoxy-(N-methylacetamido)silane, "Acetamido", andmethyldimethoxychlorosilane "Chloro". The respective RTV compositionswere then measured for tack-free time immediately upon exposing themixtures to air at ambient temperatures (25° C.) and after several daysof aging at 25° C., 50° C. and 100° C. The following results wereobtained:

    ______________________________________                                        Aging (days)                                                                             ambient      50° C.                                                                         100° C.                                ______________________________________                                        Chloro TFT (hours)                                                            0          no cure*                                                           Acetamido TFT (hours)                                                         0          5            --      --                                            6          5            5       5                                             14         5            5       5                                             ______________________________________                                         *When the RTV composition was exposed to atmospheric moisture it did not      cure. The RTV composition remained liquid.                               

The above results show that the dimethoxy-terminatedpolydimethylsiloxane based on the use ofmethyldimethoxy-(N-methylacetamido)silane scavenger provides an improvedRTV composition as compared to the RTV composition based on the use ofmethyldimethoxychlorosilane. The above mixture is found to remainsubstantially the same after a six day and 14 day aging period atambient temperature and temperatures of 50° C. and 100° C. as the resultof exhibiting substantially the same TFT.

A mixture of 100 parts of the above silanol-terminatedpolydimethylsiloxane, 2 parts ofmethyldimethoxy-(N-methylacetamido)silane and 0.5 part oftrimethoxysilylpropyltetramethylguanidine was mixed for 15 minutes undersubstantially anhydrous conditions and there was then added 0.13 part ofdibutyltindimethoxide to the resulting mixture. The mixture was thenmixed for an additional 15 minutes and then the stability of theresulting RTV was measured over a period of up to 14 days at ambienttemperatures, 50° C. and 100° C. The following results were obtained:

    ______________________________________                                        Acetamido TFT (min)                                                           Aging (days)                                                                             Ambient      50° C.                                                                         100° C.                                ______________________________________                                        0          25           --      --                                            6          20           20      20                                            14         20           20      80                                            ______________________________________                                    

The above results show that the acetamido RTV of the present inventionhas a faster TFT as compared to the RTV composition free of thetrimethoxysilylpropyltetramethylguanidine curing accelerator.

EXAMPLE 2

Additional one-package room temperature vulcanizable compositions wereprepared consisting of 85 parts of the dimethoxy terminatedpolydimethylsiloxane and 15 parts of the octamethylcyclotetrasiloxanetreated fumed silica filler and 0.23 part of dibutyltindiacetate. Theseroom temperature vulcanizable compositions were prepared undersubstantially anhydrous conditions and the polymer filler blend wasinitially injected into plastic tubes followed by the incorporation of 0to 1.5 part of methyldimethoxy-(N-methylacetamido)silane.

The dimethoxy terminated polydimethylsiloxane having the same formula asshown in Example 1 was prepared by effecting reaction between 100 partsof the silanol terminated polydimethylsiloxane of Example 1 and 30 partsof methyltrimethoxysilane in the presence of 0.65 part ofdi-n-hexylamine. The mixture was agitated and heated under dry nitrogenat a temperature of 80° C. for approximately 1 hour and the excessmethyltrimethoxysilane was then stripped from the mixture.

RTV compositions were prepared from the above ingredients containing 0,0.5 and up to 1.5 parts of the methyldimethoxy-(N-methylacetamido)silanewhich was added along with the dibutyltindiacetate to plastic tubescontaining the blend of the dimethoxy terminated polydimethylsiloxaneand the treated fumed silica which was formed by mixing the polymer andfiller for 2 hours under nitrogen and then stripped under full vacuumprior to injection into the plastic tubes. The following results wereobtained, where TFT (minutes) was determined as in Example 1 andDurometer Hardness (Shore A) indicates a complete cure:

    ______________________________________                                                TFT (min)      Durometer                                              Age (days)                                                                              25° C.                                                                            100° C.                                                                          25° C.                                                                       100° C.                           ______________________________________                                        0 Part Scavenging Silane                                                      0         30         --        --    --                                       1         gelled in tube                                                                           --        --    --                                       2         --         --        --    --                                       0.5 Part Scavenging Silane                                                    0         >60        --        --    --                                       1         60         35        28    30                                       2         gelled in tube                                                                           --        --    --                                       1 Part Scavenging Silane                                                      0         50         --        --    --                                       1         35         30        34    34                                       2         --         30        --    29                                       ______________________________________                                    

Additional RTV compositions were prepared containing up to 1.5 parts ofthe scavenging silane per 100 parts of the RTV composition whichexhibited substantially the same tack-free time and cure as shown forthe 1 part level. The above results further demonstrate that stable RTVcompositions can be obtained when a stabilizing amount of scavengingsilane, for example, methyldimethoxy-(N-methylacetamido)silane isutilized in combination with an effective amount of curing acceleratordi-n-hexylamine.

EXAMPLE 3

An RTV composition was prepared under substantially anhydrous conditionsby agitating a mixture of 85 parts of the silanol-terminatedpolydimethylsiloxane, and 15 parts of the treated filler for 2 hours at130° C. under vacuum. After cooling to room temperature, there was added2.5 parts of methyldimethoxy-(N-methylacetamido)silane, and 0.27 part ofa substituted guanidine having the formula,

    [(CH.sub.3).sub.2 N].sub.2 C═N-C.sub.4 H.sub.9.

In addition, 2 parts of a titanium chelate, 1,3-propanedioxytitaniumbis(ethylacetoacetonate), was used as a condensation catalyst. Unlikethe procedure of Example 1, here the condensation catalyst, scavengerand the curing accelerator were added to the polymer at the same time.There was obtained an RTV composition, hereinafter referred to as RTV"A".

The above procedure was repeated, except that 1.0 part of the sametitanium chelate was used to make RTV "B", and 0.23 part of the titaniumchelate to make RTV "C". In addition, the same RTV compositions wereprepared free of the substituted guanidine. The tackfree times (TFT) ofthe various RTV compositions were then measured at ambient conditionsimmediately upon mixing and after 24 hours at 100° C. The followingresults were obtained, where "chelate" is the titanium chelate used:

                  TABLE I                                                         ______________________________________                                        Chelate                  TFT (hrs)                                            RTV     Parts    Guanidine   25° C.                                                                       *100° C.                            ______________________________________                                        A       2.0      0.27        5     4                                                           0           4     3                                          B       1.0      0.27        4     4                                                           0           --    4                                          C       0.23     0.27        5     3                                                           0           4     4                                          ______________________________________                                         *After 24 hours shelf aging.                                             

The above procedure was repeated with RTV "B", except that 2.0 parts ofmethyltrimethoxysilane was added to the mixture. The TFT's of the RTV's,with and without substituted guanidine was measured up to 3 days at 25°C. and 100° C. The following results were obtained:

                  TABLE II                                                        ______________________________________                                                          TFT (hrs)                                                   Age (days)                                                                              Guanidine     25° C.                                                                          100° C.                               ______________________________________                                        1         0.27          .58      .58                                                    0             >15      4                                            2         0.27          2.26     .58                                                    0             >15      2.3                                          3         0.27          No cure  1.4                                                    0             No cure  2.4                                          ______________________________________                                    

Table I shows that RTV compositions of the present invention containingtitanium chelate as a condensation catalyst and free of cross-linkingsilane remained stable in the presence or absence of an alkyl guanidine.Table II shows that faster TFT's can be obtained if a cross-linkingsilane is used with alkyl guanidine. Further, a commercially availabletitanium chelate RTV composition, such as shown by Smith et al U.S. Pat.No. 3,689,454 did not cure after being subjected to the same 100° C.accelerated aging test for 24 hours.

EXAMPLE 4

A room temperature vulcanizable composition "Acetamido", was prepared bymixing under substantially anhydrous conditions, 85 parts of the silanolterminated polydimethylsiloxane of Example 1, 15 parts ofoctamethylcyclotetrasiloxane treated fumed silica of Example 2, 2.8parts of methyldimethoxy-(N-methylacetamido)silane, 2 partsmethyltrimethoxysilane and 0.1 part of dibutyltindimethoxide. There wasadded to the aforementioned room temperature vulcanizable compositionprepared under substantially anhydrous conditions, various amounts oftrimethoxysilylpropyltetramethylguanidine to determine the effectivenessof this material as a stabilizer-curing accelerator for theaforementioned Acetamido RTV composition at ambient temperatures and ataccelerated aging temperatures after a 1 day shelf age at ambienttemperatures, 50° C. and 100° C. Tack-free time (TFT) in minutes, andDurometer Hardness (Shore A) were measured. In addition, a commerciallyavailable one-package RTV containing methyltriacetoxysilane "Acetoxy"was used as a control. The mixing sequence was the same as in Example 3.The following results were obtained as shown in Table III:

                  TABLE III                                                       ______________________________________                                                                      Durometer Hardness                              Leav- Guani-  TFT (min)       (Shore A)                                       ing   dine    1 day age       1 day age                                       Group (Parts) R.T.    50° C.                                                                       100° C.                                                                      R.T. 50° C.                                                                       100° C.                   ______________________________________                                        Acet- 0.00    >300    120   33     0    0     0                               amido 0.05    105     95    113    2    2     5                                     0.10    106     55    88     9   10     9                                     0.20    27      25    48    21   23    24                                     0.30    28      25    18    22   24    28                                     0.40    30      25    18    23   25    25                               Acet-                                                                         oxy   0.00    20      15    10    25   29    30                               ______________________________________                                    

A comparison of the results obtained for Acetamido and Acetoxy as setforth in Table III clearly illustrates that the non-corrosivesubstantially odor-free RTV compositions of the present invention canprovide fast cure fully equivalent to commercially available one-partacetoxy RTV sealants without the serious disadvantages of generatingcorrosive, odoriferous cure byproducts.

The above data indicate that the curing accelerator as previouslydefined also acts as a stabilizer with dibutyltindimethoxide catalyst.

EXAMPLE 5

The procedure of Example 4 was repeated, except that there was utilized85 parts of the silanol-terminated polydimethylsiloxane, 15 parts of theoctamethylcyclotetrasiloxane treated silica filler, 2.8 parts of themethyldimethoxy-(N-methylacetamido)silane, 0.4 part oftrimethoxysilylpropyltetramethylguanidine, 2.6 parts of themethyltrimethoxysilane and 0.1 part of dibutyltindimethoxide.

The above room temperature vulcanizable composition was then evaluatedfor stability and other physical properties after a two day aging periodat room temperature and at 100° C. The following results were obtained,where TFT is as previously defined:

                  TABLE IV                                                        ______________________________________                                                  Shelf Age Time                                                                             RT     100° C.                                  ______________________________________                                        TFT (min)   0 days         44     --                                                      1 day.sup.     18     18                                                      2 days         18     13                                          Shore A     2 days         38     40                                          Tensile (psi)                                                                             2 days         267    235                                         Elongation (%)                                                                            2 days         178    144                                         Die "B" Tear                                                                              2 days         26     29                                          ______________________________________                                    

The above results show that the room temperature vulcanizablecomposition of the present invention exhibits superior stability andphysical properties after an accelerated aging period at 100° C.

EXAMPLE 6

Additional silanol scavenging silanes were evaluated utilizing the baseroom temperature vulcanizable formulation of 100 parts of thesilanol-terminated polydimethylsiloxane of Example 1, 2 parts ofmethyldimethoxyisopropylamino silane, 0.5 part of thetrimethoxysilylpropyltetramethylguanidine stabilizer-curing accelerator,3 parts of the crosslinking methyltrimethoxymethylsilane and 0.13 partof dibutyltindimethoxide. The mixing sequence was the same as in Example3.

The following results were obtained:

    ______________________________________                                                 TFT (min)                                                            Shelf Age  25° C.                                                                             50° C.                                                                         100° C.                                 ______________________________________                                        0 days     22          --      --                                             3 days     45          45      No cure                                        6 days     31          41      --                                             13 days    45          73      --                                             21 days    78          >480    --                                             ______________________________________                                    

The reason for the inferior results obtained in this example was notdefinitely determined, but is believed to be attributable to adeleterious amount of methanol contamination in the cross-linker whichwas not fully scavenged.

EXAMPLE 7

A mixture of 100 parts of the silanol-terminated polydimethylsiloxane ofExample 1, 0.5 part of butyltetramethylguanidine, 2 parts ofmethyltrimethoxysilane, 2 parts of methyldimethoxymethylaminosilane and0.05 part of dibutyltindiacetate was mixed at the same time undersubstantially anhydrous conditions for a period of about 15 minutes.

The TFT of the resulting RTV composition was measured over a period of 3days at ambient temperatures, 50° C. and 100° C. The following resultswere obtained:

    ______________________________________                                                 TFT (Min)                                                            Shelf Age  RT          50° C.                                                                         100° C.                                 ______________________________________                                        1          40          40      35                                             3          40          40      45                                             ______________________________________                                    

The above results show that methyldimethoxymethylaminosilane is avaluable scavenging silane within the practice of the present inventionto provide stable RTV compositions.

EXAMPLE 8

An RTV mixture was prepared by mixing at the same time 100 parts of theabove silanol-terminated polydimethylsiloxane, 2.3 parts oftrimethoxy-(N-methylacetamido)silane, 0.5 part oftrimethoxysilylpropyltetramethylguanidine and 0.13 part ofdibutyltindimethoxide. The resulting RTV formulation was found to haveuseful properties after accelerated aging at 50° C. and 100° C. over aperiod of up to 37 days under substantially anhydrous conditions basedon the following tack-free time values:

    ______________________________________                                                 TFT (min)                                                            Shelf Age  RT          50° C.                                                                         100° C.                                 ______________________________________                                        0 days     45          --      --                                             6 days     30          30      30                                             37 days    35          35      35                                             ______________________________________                                         PG,46

EXAMPLE 9

Additional scavenging silanes, specifically,methyldimethoxyisopropenoxysilane, (Enoxy) andmethyldimethoxy-2(1-carboethoxypropenoxy)silane (Ethylacetoacetate) wereused at a 4 part level with 85 parts of the silanol-terminatedpolydimethylsiloxane and 15 parts of the treated silica filler ofExample 2.

There was further used with the Enoxy mixture 1 part ofmethyltrimethoxysilane, 0.4 part oftrimethoxysilylpropyltetramethylguanidine and 0.23 part ofdibutyltindiacetate. The Ethylacetoacetate mixture was further combinedwith 0.33 part of butyltetramethylguanidine and 0.23 part ofdibutyltindiacetate.

These RTV mixtures were shelf aged up to 2 days at room temperature and100° C., and their tack-free time were determined. The following resultswere obtained:

    ______________________________________                                        Shelf Age        TFT (Min)                                                    (days)           RT     100° C.                                        ______________________________________                                        Enoxy                                                                         0                65     --                                                    1                65     70                                                    2                65     90                                                    ______________________________________                                        Ethylacetoacetate                                                             0                10     --                                                    1                10     90                                                    2                10     85                                                    ______________________________________                                    

The above results further establish that the above scavenging silanesproduce useful RTV compositions in accordance with the practice of thepresent invention.

EXAMPLE 10

A room temperature vulcanizable composition was prepared in accordancewith the present invention by initially mixing 85 parts of thesilanol-terminated polydimethylsiloxane of Example 1 and 15 parts of thetreated fumed silica of Example 2 for 2 hours at 130° C. under vacuum.There was then added varying amounts ofmethyldimethoxydi-n-hexylaminosilane which was mixed with the silanolpolymer-filler blend for about 15 minutes prior to the introduction of0.23 part of dibutyltindiacetate which was then added into each mixtureand blended for an additional 15 minutes. The following results wereobtained, where TFT and Hardness are as defined in Example 2:

    ______________________________________                                                               Durometer                                                     TFT (min)       (Shore A)                                              Age (days)                                                                             25° C.                                                                            100° C.                                                                           25° C.                                                                        100° C.                          ______________________________________                                        2 Parts Scavenging Silane                                                     0        35         --         --     --                                      1        gelled in tube                                                       2        --         --         --     --                                      2.5 Parts Scavenging Silane                                                   0        25         --         --     --                                      1        gelled in tube                                                       2        --         --         --     --                                      3.0 Parts Scavenging Silane                                                   0        20         --         --     --                                      1        25         20         28     27                                      2        --         gelled in tube                                            3.5 Parts Scavenging Silane                                                   0        40         --         --     --                                      1        55         50         27     25                                      2        --         70         --     20                                      4 Parts Scavenging Silane                                                     0        <60        --         --     --                                      1        20         10         --     31                                      2        --         10         --     28                                      ______________________________________                                    

The above results show that the room temperature vulcanizablecompositions of the present invention can be stabilized by scavengingsilanes, such as methyldimethoxydi-n-hexylaminosilane. In addition, itwas further found that substantially equivalent results were obtainedwhen the aforementioned scavenging silane was utilized at 5 parts and 6parts per 100 parts of the RTV composition.

EXAMPLE 11

A room temperature vulcanizable composition was prepared in accordancewith the procedure of Example 3 utilizing 85 parts of asilanol-terminated polydimethylsiloxane, 15 parts ofoctamethylcyclotetrasiloxane treated fumed silica filler, 2.5 parts ofmethyldimethoxy-(N-methylacetamido)silane, 2 parts ofmethyltrimethoxysilane and 0.23 part of dibutyltindiacetate. In place ofthe guanidine curing accelerator utilized in Example 4, there wassubstituted a variety of organic amines to determine the effectivenessof these materials as curing accelerators. The amines were evaluated at2 catalytic levels, 0.72 millimole and 1.44 millimole, which isapproximately equivalent on a mole basis to 0.2 part and 0.4 part oftrimethoxysilylpropyltetramethylguanidine, per 100 parts of the base RTVmixture. The results are shown in Table V, where tack-free time (TFT)and Durometer hardness (Shore A) were measured under ambient conditionsand after an accelerated aging period at 100° C. for 1 or 2 days. Themixtures were made in plastic tubes by initially injecting the silanolpolymer-filler blend into the tubes under substantially anhydrousconditions. There was then stirred into the blend a solution ofmethyldimethoxy-(N-methylacetamido)silane scavenger,methyltrimethoxysilane cross-linker and dibutyltindiacetate catalyst.The following results were obtained:

                                      TABLE V                                     __________________________________________________________________________                                       Durometer hardness                                         Milli-                                                                            Time at        (Shore A)                                  Amine           moles                                                                             100° C. (days)                                                                TFT (Min.)                                                                            24 Hr                                                                              48 Hr                                 __________________________________________________________________________    (Me.sub.2 N).sub.2 --C═NC.sub.3 H.sub.6 Si(OMe).sub.3                                     1.44                                                                              1      27      34   35                                      "             "   2      35      30   32                                      "             0.72                                                                              1      40      28   30                                      "             "   2      .sup. >24 hr                                                                           7   13                                    (Me.sub.2 N).sub.2 --C═NC.sub.4 H.sub.9                                                   1.44                                                                              1      25      30   35                                      "             "   2      30      34   39                                      "             0.72                                                                              1      60      33   34                                      "             "   2      .sup. >24 hr                                                                           3    6                                    H.sub.2 NC.sub.3 H.sub.6 Si(OMe).sub.3                                                        1.44                                                                              1      45      37   37                                      "             "   2      50      28   32                                      "             0.72                                                                              1      40      20   22                                      "             "   2      No cure --   --                                    Di-n-hexylamine 1.44                                                                              1      40      30   32                                       "            "   2      30      25   27                                    H.sub.2 NC.sub.3 H.sub.6 Si(OEt).sub.3                                                        1.44                                                                              1      37      31   34                                      "             "   2      160     21   --                                      "             0.72                                                                              1      40      23   26                                      "             "   2      .sup. >24 hr                                                                           3    9                                    Cyclohexylamine 1.44                                                                              1      60      24   27                                      "             "   2      50      21   --                                      "             0.72                                                                              1      60      18   21                                      "             "   2      70      23   27                                    Jeffamine T-403*                                                                              1.44                                                                              1      55      34   37                                      "             "   2      160     21   --                                    H.sub.2 NC.sub.2 H.sub.4 NHC.sub.3 H.sub.6 Si(OMe).sub.3                                      1.44                                                                              1      45      30   36                                      "             "   2      Gelled in tube                                                                        --   --                                      "             0.72                                                                              1      105     17   22                                      "             "   2       2      No cure                                                                            --                                     *A tris(2aminopropyl)triol                                               

    Tetramethylpiperidine                                                                         1.44                                                                              1      60      19   21                                      "             "   2      30      18   20                                    Piperidine      1.44                                                                              1      40      26   29                                       "            "   2        >8 hr  6    9                                    DABCO*          1.44                                                                              1      55      16   23                                      "             "   2      35      13   --                                    N--methylmorpholine                                                                           1.44                                                                              1      55       8   14                                      "             "   2      35      11   --                                    N,N'--dimethylethylenediamine                                                                 1.44                                                                              1      55       9   18                                      "             "   2      35      12   --                                    N--methylpiperidine                                                                           1.44                                                                              1      Gelled in tube                                                                        --   --                                      "             "   2      at R.T. --   --                                    n-hexylamine    1.44                                                                              1      105     21   23                                      "             "   2      No cure --   --                                    tributylamine   1.44                                                                              1      70      18   20                                      "             "   2      No cure --   --                                    __________________________________________________________________________     *1,4-diazabicyclo[2.2.2]octane                                           

A higher level of candidate amine stabilizers was evaluated with thesame room temperature vulcanizable composition along with a homologousseries of dialkylamines. The results are shown in Table VI below:

                                      TABLE VI                                    __________________________________________________________________________                                    Durometer hardness                                           Milli-                                                                            Time at      (Shore A)                                     Amine          moles                                                                             100° C. (days)                                                                TFT (Min.)                                                                          24 Hr                                                                              48 Hr                                    __________________________________________________________________________    H.sub.2 NC.sub.3 H.sub.6 Si(OEt).sub.3                                                       2.88                                                                              1      35    31   31                                       "              "   2      55    25   28                                       H.sub.2 NC.sub.3 H.sub.6 Si(OMe).sub.3                                                       2.88                                                                              1      35    30   20                                       "              "   2      105   34   25                                       H.sub.2 NC.sub.2 H.sub.4 NHC.sub.3 H.sub.6 Si(OMe).sub.3                                     2.88                                                                              1      70    22   23                                       "              "   2            No cure                                       Jeffamine T-403                                                                              2.88                                                                              1      60    18   19                                       "              "   2            No cure                                       Tetramethylpiperidine                                                                        2.88                                                                              1      35    28   28                                       "              "   2      50    28   29                                       Cyclohexylamine                                                                              2.88                                                                              1      60    15   16                                       "              "   2      50    22   24                                       Di-n-hexylamine                                                                              2.88                                                                              1      40    34   35                                       "              "   2      40    37   39                                       Dibutylamine   2.88                                                                              1      45    18   21                                       "              "   2      40    16   19                                       Dioctylamine   2.88                                                                              1      40    36   35                                       "              "   2      45    38   37                                       Dicyclohexylamine                                                                            2.88                                                                              1      40    33   33                                       "              "   2      45    34   36                                       Hexamethoxymethylmelamine                                                                    2.88                                                                              1      50    20   --                                       "              "   2      17    18   --                                       Methylphenylamine                                                                            2.88                                                                              1      20    30   --                                       "              "   2      15    29   --                                       Diphenylamine  2.88                                                                              1      50    10   --                                       "              "   2      70    13                                            Diisopropylamine                                                                             2.88                                                                              1      35    27   --                                       "              "   2      50    30   --                                       Diisobutylamine                                                                              2.88                                                                              1      35    17   --                                       "              "   2      50    19   --                                       hexylamine                                                                    Diethylamine   2.88                                                                              1      50    23   26                                       "              "   2      45    20   23                                       Dipropylamine  2.88                                                                              1      50    21   23                                       "              "   2      45    18   21                                       __________________________________________________________________________

The above results show that effective cure acceleration of the RTVcomposition can be achieved using higher levels of various organicamines including a variety of dialkyl amines. In addition, certaintertiary amines, for example, N-methylpiperidine and N,N-dimethylanilinewere found to be ineffective as cure accelerators at the 2.88 millimolelevel.

Although the above examples are directed to only a few of the very manyvariables which can be utilized in the practice of the presentinvention, it should be understood that the present invention isdirected to a much broader variety of room temperature vulcanizablecompositions based on the use of a wide variety of silanol-terminated orpolyalkoxy-terminated organopolysiloxanes, silane scavengers,cross-linking silanes, mixtures of silane scavengers and cross-linkingsilanes, as well as one or more of the several substituted guanidine andamine curing accelerators and condensation catalysts as previouslydescribed.

What we claim as new and desire to secure by Letters Patent of theUnited States is:
 1. A stable, one-package, substantially anhydrous andsubstantially acid-free, room temperature vulcanizableorganopolysiloxane composition stable under ambient conditions in thesubstantial absence of moisture over an extended period of time andconvertible to a tack-free elastomer comprising: (1) anorganopolysiloxane wherein the silicon atom at each polymer chain end isterminated with at least 2 alkoxy radicals; (2) an effective amount of acondensation catalyst; (3) a stabilizing amount of silane scavenger forhydroxy functional groups having the formula ##STR14## where R¹ is aC.sub.(1-8) aliphatic organic radical selected from the group consistingof alkyl, alkylether, alkylester, alkylketone, and alkylcyano radicals,or a C.sub.(7-13) aralkyl radical, R² is a C.sub.(1-13) monovalentsubstituted or unsubstituted hydrocarbon radical, X is a hydrolyzableleaving group selected from the group consisting of amido, amino,carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato andureido radicals and, c is a whole number equal to 0 to 3 inclusive, f isan integer equal to 1 to 4 inclusive and the sum of c+f is equal to 1 to4 inclusive; and where X is enoxy or amido, (4) an effective amount of acuring accelerator selected from the group consisting of substitutedguanidines, amines and mixtures thereof.
 2. The composition of claim 1wherein the silane has the formula ##STR15## where R¹ is a C.sub.(1-8)aliphatic organic radical selected from the group consisting of alkyl,alkylether, alkylester, alkylketone and alkylcyano radicals, or aC.sub.(7-13) aralkyl radical, R² is a C.sub.(1-13) monovalentsubstituted or unsubstituted hydrocarbon radical, X is a hydrolyzableleaving group selected from the group consisting of amido, amino,carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato andureido radicals; and, a is an integer equal to 1 to 2 inclusive, b is awhole number equal to 0 to 1 inclusive, and the sum of b+a is equal to 1to 2 inclusive and the silane is both the silane scavenger for hydroxyfunctional groups and a polyalkoxysilane cross-linking agent forterminating the silicon atom at each organopolysiloxane chain end withat least two alkoxy radicals.
 3. A stable, one-package, substantiallyanhydrous and substantially acid-free, room temperature vulcanizableorganopolysiloxane composition stable under ambient conditions in thesubstantial absence of moisture over an extended period of time andconvertible to a tack-free elastomer comprising: (1) anorganopolysiloxane wherein the silicon atom at each polymer chain end isterminated with at least 2 alkoxy radicals; (2) an effective amount of acondensation catalyst; (3) a stabilizing amount of silane scavenger forhydroxy functional groups having the formula ##STR16## where R¹ is aC.sub.(1-8) aliphatic organic radical selected from the group consistingof alkyl, alkylether, alkylester, alkylketone and alkylcyano radicals,or a C.sub.(7-13) aralkyl radical, R² is a C.sub.(1-13) monovalentsubstituted or unsubstituted hydrocarbon radical, X is a hydrolyzableleaving group selected from the group consisting of amido, amino,carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato andureido radicals and, c is a whole number equal to 0 to 3 inclusive, f isan integer equal to 1 to 4 inclusive and the sum of c+f is equal to 1 to4 inclusive; and (4) an effective amount of a curing acceleratorselected from the group consisting of substituted guanidines, amines andmixtures thereof.
 4. A one-package, room temperature vulcanizablepolyalkoxy-terminated organopolysiloxane composition in accordance withclaim 1, where the polyalkoxy-terminated organopolysiloxane has theformula ##STR17## where R is a C.sub.(1-13) monovalent substituted orunsubstituted hydrocarbon radical, R¹ is a C.sub.(1-8) aliphatic organicradical selected from the group consisting of alkyl, alkylether,alkylester, alkylketone and alkylcyano radicals, or a C.sub.(7-13)aralkyl radical, R² is a C.sub.(1-13) monovalent substituted orunsubstituted hydrocarbon radical, X is a hydrolyzable leaving groupselected from the group consisting of amido, amino, carbamato, enoxy,imidato, isocyanato, oximato, thioisocyanato and ureido radicals and, bis a whole number equal to 0 or 1, e is a whole number equal to 0 or 1inclusive and the sum of b+e is equal to 0 or 1 inclusive, and n is aninteger having a value of from about 50 to about 2500 inclusive.
 5. Aroom temperature vulcanizable composition in accordance with claim 1having an effective amount of a cross-linking silane of the formula##STR18## where R¹ is a C.sub.(1-8) aliphatic organic radical selectedfrom the group consisting of alkyl, alkylether, alkylester, alkylketoneand alkylcyano radicals, or a C.sub.(7-13) aralkyl radical, R² is aC.sub.(1-13) monovalent substituted or unsubstituted hydrocarbonradical, and b is a whole number equal to 0 or
 1. 6. A room temperaturevulcanizable composition in accordance with claim 1, where the silanescavenger is methyldimethoxy(N-methylacetamido)silane.
 7. A roomtemperature vulcanizable composition in accordance with claim 1, whichcontains a tin compound as the condensation catalyst.
 8. A roomtemperature vulcanizable composition in accordance with claim 4, whereR, R¹ and R² are methyl and which has a tin compound as a condensationcatalyst.
 9. A room temperature vulcanizable composition in accordancewith claim 1, containing an effective amount of a curing acceleratorselected from the group consisting of substituted guanidines, amines andmixtures thereof.
 10. A stable, one-package, substantially anhydrous andsubstantially acid-free, room temperature vulcanizable compositioncomprising a polymethoxy-terminated polydimethylsiloxane, an effectiveamount of a tin containing condensation catalyst, and a stabilizingamount of a polymethoxydi-n-hexylaminosilane.
 11. A stable, one-package,substantially anhydrous and substantially acid-free, room temperaturevulcanizable composition comprising a polymethoxy-terminatedpolydimethylsiloxane, and effective amount of a tin containingcondensation catalyst, an effective amount oftrimethoxysilylpropyltetramethylguanidine curing accelerator and astabilizing amount of a polymethoxyacetamidosilane.
 12. An RTVcomposition in accordance with claim 10 containing dibutyltindiacetate.13. An RTV composition in accordance with claim 10 containing apolymethoxysilane cross-linking agent.
 14. A stable and substantiallyacid-free, one-package room temperature vulcanizablepolyalkoxy-terminated organopolysiloxane composition curable underambient conditions to a tack-free elastomer over an extended period oftime comprising on a weight basis,(i) 100 parts of a substantiallysilanol-free polyalkoxysiloxydiorganopolysiloxane of the formula##STR19## (ii) 0 to 10 parts of a cross-linking polyalkoxysilane of theformula ##STR20## (iii) an effective amount of a condensation catalyst,and (iv) a stabilizing amount of a silane scavenger for hydroxyfunctional groups having the formula ##STR21## where R is a C.sub.(1-13)monovalent substituted or unsubstituted hydrocarbon radical, R¹ is aC.sub.(1-8) aliphatic organic radical selected from the group consistingof alkyl, alkylether, alkylester, alkylketone and alkylcyano radicals,or a C.sub.(7-13) aralkyl radical, R² is a C.sub.(1-13) monovalentsubstituted or unsubstituted hydrocarbon radical, X is a hydrolyzableleaving group selected from the group consisting of amido, amino,carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato andureido radicals and, b is a whole number equal to 0 or 1, e is a wholenumber equal to 0 to 1 inclusive, and the sum of b+e is equal to 0 or 1inclusive, and n is an integer having a value of from about 50 to about2500 inclusive, c is a whole number equal to 0 to 3 inclusive, f is aninteger equal to 1 to 4 inclusive and the sum of c+f is equal to 1 to 4inclusive; and (v) where X is enoxy, 0.1 to 5 parts of a curingaccelerator selected from the group consisting of substitutedguanidines, amines and mixtures thereof.
 15. A room temperaturevulcanizable polyalkoxy-terminated organopolysiloxane composition inaccordance with claim 14 containing an effective amount of a curingaccelerator selected from the group consisting of substitutedguanidines, amines and mixtures thereof.
 16. A one-package roomtemperature vulcanizable composition in accordance with claim 14, whereR, R¹ and R² are methyl.
 17. A one-package room temperature vulcanizablecomposition in accordance with claim 14, where the condensation catalystis a tin compound.
 18. A stable and substantially acid-free,one-package, room temperature vulcanizable composition comprising apolymethoxy-terminated polydimethylsiloxane, a polymethoxysilane, aneffective amount of a curing accelerator selected from the groupconsisting of substituted guanidines, amines and mixtures thereof, aneffective amount of a tin compound condensation catalyst, and astabilizing amount of a silane scavenger for hydroxy functional groupshaving at least one hydrolyzable leaving group selected from the groupconsisting of amido, amino, carbamato, enoxy, imidato, isocyanato,oximato, thioisocyanato and ureido radicals.
 19. A one-package roomtemperature vulcanizable composition in accordance with claim 18, wherethe polymethoxysilane is methyltrimethoxysilane.
 20. A one-package RTVin accordance with claim 18, where the substituted quanidine isbutyltetramethylguanidine.
 21. A one-package RTV in accordance withclaim 18, where the organic amine is a dialkylamine.
 22. A substantiallyacid-free room temperature vulcanizable composition comprisingmethyldimethoxysiloxy terminated polydimethylsiloxane, a reinforcingamount of octamethylcyclotetrasiloxane treated silica filler, aneffective amount of dibutyltindiacetate condensation catalyst, a cureaccelerating amount of trimethoxysilylpropyltetramethylguanidine and anexcess of up to 3% by weight, based on the weight of thepolydimethylsiloxane of methyldimethoxy-(N-methylacetamido)silane.
 23. Aone-package, stable room temperature vulcanizable composition inaccordance with claim 22, having as the silane in place of the acetamidoan excess of up to 3% by weight, based on the weight of thepolydimethylsiloxane of methyldimethoxyisopropenoxysilane.
 24. A roomtemperature vulcanizable composition in accordance with claim 22 havingup to 10 parts of methyltrimethoxysilane per 100 parts of thepolydimethylsiloxane.
 25. A room temperature vulcanizable composition inaccordance with claim 22 having an effective amount of di-n-hexylaminecuring accelerator in place oftrimethoxysilylpropyltetramethylguanidine.
 26. In the method of making asubstantially acid-free room temperature vulcanizable organopolysiloxanecomposition under substantially anhydrous conditions utilizing aneffective amount of a condensation catalyst with an organopolysiloxanewherein the silicon atom at each polymer chain end is terminated with atleast two alkoxy radicals, the improvement which comprises adding tosaid polyalkoxy-terminated organopolysiloxane (1) a stabilizing amountof a silane scavenger for hydroxy functional groups of the formula##STR22## where R¹ is a C.sub.(1-8) aliphatic organic radical selectedfrom the group consisting of alkyl, alkylether, alkylester, alkylketoneand alkylcyano radicals, or a C.sub.(7-13) aralkyl radical, R² is aC.sub.(1-13) monovalent substituted or unsubstituted hydrocarbonradical, X is a hydrolyzable leaving group selected from the groupconsisting of amido, amino, carbamato, enoxy, imidato, isocyanato,oximato, thioisocyanato and ureido radicals and, c is a whole numberequal to 0 to 3 inclusive, f is an integer equal to 1 to 4 inclusive,and the sum of c+f is equal to 1 to 4 inclusive, and (2) an effectiveamount of a condensation catalyst, whereby improved stability isachieved in the resulting room temperature vulcanizableorganopolysiloxane composition, and (3) where X is enoxy, adding beforeor with the scavenger an effective amount of a curing acceleratorselected from the group consisting of substituted guanidines, amines andmixtures thereof.
 27. A method in accordance with claim 26, where thsilane scavenger is methyldimethoxy-(N-methylacetamido)silane.
 28. Amethod in accordance with claim 26, where the silane scavenger ismethyldimethoxyisopropenoxysilane.
 29. A method in accordance with claim26, utilizing a stabilizing amount of methyltriisopropenoxysilane and aneffective amount of methyltrimethoxysilane.
 30. A method in accordancewith claim 26, using an effective amount of dibutyltindiacetate as thecondensation catalyst.
 31. A room temperature vulcanizable compositionin accordance with claim 5, where the cross-linking silane ismethyltrimethoxysilane, the condensation catalyst is dibutyltindiacetateor dibutyltindilaurate, and the curing accelerator is di-n-hexylamine ordi-n-butylamine.
 32. A one-package room temperature vulcanizablecomposition in accordance with claim 17, where the tin compound isdibutyltindiacetate or dibutyltindilaurate, the cross-linking silane ismethyltrimethoxysilane and the curing accelerator is di-n-hexylamine ordi-n-butylamine.
 33. A one-package room temperature vulcanizablecomposition in accordance with claim 19, where the tin compound isdibutyltindiacetate or dibutyltindilaurate, and the curing acceleratoris di-n-hexylamine or di-n-butylamine.
 34. A method in accordance withclaim 30, using an effective amount of methyltrimethoxysilane, and aneffective amount of di-n-hexylamine or di-n-butylamine as the curingaccelerator.
 35. A method in accordance with claim 26, using aneffective amount of dibutyltindilaurate as the condensation catalyst.36. A method in accordance with claim 35, using an effective amount ofmethyltrimethoxysilane, and an effective amount of di-n-hexylamine ordi-n-butylamine as the curing accelerator.